This invention relates to a method of manufacture and in particular relates to a method of manufacturing cylindrical metal structures having discrete internal contours.
Cylindrical metal structures are used throughout industry in a wide variety of applications. Such structures are particularly useful in the construction of parts for gas turbine engines including the construction of rotor spools. Typically, rotor spools for gas turbine engines have been machined from thick-walled, heat treated, metal cylindrical forgings of rectangular or other simple cross-section having an axial length substantially equal to that of the rotor, an internal radial diameter slightly less than that of the rotor and a wall thickness slightly greater than the thickest part of the rotor. The cross-sections of a typical starting forging 1 and rotor 18 to be machined therefrom is shown in FIG. 1. In this machining operation, a lathe is used to cut away excess material from the starting metal cylindrical forging in order to achieve the desired internal contour. Typically in such an operation as much as 80% of the original starting material may have to be removed in order to achieve the desired internal contour. Accordingly, such prior art machining methods have been found to be both extremely time consuming and wasteful. This problem is particularly acute in the construction of rotors for use in gas turbine engines because of the relatively expensive, high-temperature metal alloys used and the relatively high cost to machine these tough alloys.